Fix(test): Update error message assertions for unsupported content type tests (#12901)

### What problem does this PR solve?

This commit updates test cases for create, delete, and update dataset
endpoints to expect consistent error messages when an unsupported
content type is provided.

### Type of change

- [x] Bug Fix (test)

test/testcases/test_http_api/test_dataset_management/test_create_dataset.py

@@ -53,7 +53,7 @@ class TestRquest:
         BAD_CONTENT_TYPE = "text/xml"
         res = create_dataset(HttpApiAuth, {"name": "bad_content_type"}, headers={"Content-Type": BAD_CONTENT_TYPE})
         assert res["code"] == 101, res
-        assert "Field: <name>" in res["message"], res
+        assert res["message"] == f"Unsupported content type: Expected application/json, got {BAD_CONTENT_TYPE}", res
 
     @pytest.mark.p3
     @pytest.mark.parametrize(

test/testcases/test_http_api/test_dataset_management/test_delete_datasets.py

@@ -51,7 +51,7 @@ class TestRquest:
         BAD_CONTENT_TYPE = "text/xml"
         res = delete_datasets(HttpApiAuth, headers={"Content-Type": BAD_CONTENT_TYPE})
         assert res["code"] == 101, res
-        assert "Field: <ids>" in res["message"], res
+        assert res["message"] == f"Unsupported content type: Expected application/json, got {BAD_CONTENT_TYPE}", res
 
     @pytest.mark.p3
     @pytest.mark.parametrize(

test/testcases/test_http_api/test_dataset_management/test_update_dataset.py

@@ -56,7 +56,7 @@ class TestRquest:
         BAD_CONTENT_TYPE = "text/xml"
         res = update_dataset(HttpApiAuth, dataset_id, {"name": "bad_content_type"}, headers={"Content-Type": BAD_CONTENT_TYPE})
         assert res["code"] == 101, res
-        assert res["message"] == "No properties were modified", res
+        assert res["message"] == f"Unsupported content type: Expected application/json, got {BAD_CONTENT_TYPE}", res
 
     @pytest.mark.p3
     @pytest.mark.parametrize(